Propulsion system for an aircraft

Abstract

An aeronautical thruster of longitudinal axis includes a hub, an annular row of unducted upstream rotor blades, and an annular row of unducted downstream stator blades. The annular row of downstream stator blades includes at least one downstream stator blade of a first type, each of which is located about the longitudinal axis in a first angular sector about the longitudinal axis. Each downstream stator blade of the first type has a fixed pitch. The annular row of downstream blades further includes at least one downstream stator blade of a second type, each of which is located about the longitudinal axis outside said first angular sector, wherein each downstream stator blade of the second type has a variable pitch.

1 . An aeronautical thruster having a longitudinal axis and comprising a hub, an annular row of unducted upstream rotor blades, and an annular row of unducted downstream stator blades, wherein the annular row of downstream stator blades comprises:
 at least one downstream stator blade of a first type, each downstream stator blade of the first type being located around the longitudinal axis in a first angular sector around the longitudinal axis, each downstream stator blade of the first type having a fixed pitch, and   at least one downstream stator blade of a second type, each downstream stator blade of the second type being located around the longitudinal axis outside said first angular sector, each downstream stator blade of the second type having a variable pitch.   
     
     
         2 . The aeronautical thruster according to  claim 1 , wherein the first angular sector extends over an angular range less than or equal to 180°. 
     
     
         3 . The aeronautical thruster according to  claim 1 , wherein the annular row of downstream stator blades comprises between one and six downstream stator blades of the first type. 
     
     
         4 . The aeronautical thruster according to  claim 1 , wherein at least two downstream stator blades of the first type have a different pitch angle (γ). 
     
     
         5 . The aeronautical thruster according to  claim 4 , wherein the difference between the pitch angle of said two downstream stator blades of the first type is less than 120°, preferably less than 60°. 
     
     
         6 . The aeronautical thruster according to  claim 4 , wherein said two downstream stator blades of the first type are circumferentially consecutive, the difference between the pitch angle of said two downstream stator blades of the first type being less than 45°. 
     
     
         7 . The aeronautical thruster according to  claim 1 , wherein at least two downstream stator blades of the first type have an identical pitch angle (γ). 
     
     
         8 . The aeronautical thruster according to  claim 1 , wherein each downstream stator blade of the first type has identical dimensional characteristics. 
     
     
         9 . The aeronautical thruster according to  claim 1 , wherein at least two downstream stator blades of the first type have different dimensional characteristics. 
     
     
         10 . The aeronautical thruster according to  claim 1 , wherein at least two downstream stator blades of the second type have a different pitch angle (γ). 
     
     
         11 . The aeronautical thruster according to  claim 10 , wherein the difference between the pitch angle of said two downstream stator blades of the second type is less than 120°. 
     
     
         12 . The aeronautical thruster according to  claim 10 , wherein said two downstream stator blades of the second type are circumferentially consecutive, the difference between the pitch angle of said two downstream stator blades of the second type being less than 20°. 
     
     
         13 . The aeronautical thruster according to  claim 1 , in which each of the downstream stator blades of the first type and/or each of the downstream stator blades of the second type has a pitch angle (γ) which is determined as a function of the angular position of the downstream stator blade of the first type respectively of the second type, about the longitudinal axis, in particular according to a linear, parabolic, sinusoidal, logarithmic, or exponential law. 
     
     
         14 . The aeronautical thruster according to  claim 1 , wherein each downstream stator blade of the second type has a pitch angle (γ) different from the pitch angle (γ) of the circumferentially adjacent downstream stator blade(s) of the second type. 
     
     
         15 . The aeronautical thruster according to  claim 1 , wherein each downstream stator blade comprises a stack of sections in the radial direction, each section comprising an upstream leading edge and a downstream trailing edge between which extend a lower surface line and an upper surface line so as to define an aerodynamic profile, each section further comprising a chord defined by a portion of a straight line connecting the leading edge to the trailing edge, and wherein for each pair of a first downstream stator blade and a second downstream stator blade, each section of the first downstream stator blade has an identical aerodynamic profile to a corresponding section of the second downstream stator blade over an upstream end portion that extends longitudinally over a relative chord length of between 5% and 50%, said corresponding sections of the first downstream stator blade and the second downstream stator blade each being disposed at the same radial distance from the longitudinal axis. 
     
     
         16 . A propulsion system for an aircraft, the propulsion system comprising the aeronautical thruster according to  claim 1  and a pylon configured to attach the aeronautical thruster to the aircraft, the pylon extending in a direction comprising at least one radial component from a radially inner end by which the pylon is connected to the hub of the aeronautical thruster, the first angular sector being centred on a longitudinal median plane of the pylon. 
     
     
         17 . The propulsion system according to  claim 16 , in which the pylon comprises a leading edge and a trailing edge between which extend on each side in the circumferential direction an upper surface face and a lower surface face, the upper surface face and the lower surface face of the pylon being at least on an upstream portion of the pylon, circumferentially disposed on either side of a radial plane defined by the longitudinal axis and a radial axis passing, at least in part, through the leading edge of the pylon, the annular row of downstream stator blades of the aeronautical thruster comprising:
 a first group comprising one or more downstream blades of the first type which each have a downstream end located circumferentially on the same side as the upper surface face of the pylon with respect to the radial plane the first group comprising at least the downstream stator blade of the first type which is circumferentially closest to the radial plane and whose downstream end is located circumferentially on the same side as the upper surface face of the pylon with respect to the radial plane   a second group comprising one or more downstream blade(s) of the first type, each of which has a downstream end located circumferentially on the same side as the lower surface face of the pylon with respect to the radial plane, the second group comprising at least the first type downstream stator blade which is circumferentially closest to the radial plane and whose downstream end is located circumferentially on the same side as the lower surface face of the pylon with respect to the radial plane and   wherein each first type downstream stator blade of the first group is in a closed-pitch configuration relative to the first type downstream stator blades of the second group.   
     
     
         18 . The propulsion system of  claim 16 , wherein the pylon is connected to one of the downstream stator blades so as to form a unitary aerodynamic assembly. 
     
     
         19 . A method of operating the aeronautical thruster according to  claim 1 , the method comprising adjusting the pitch angle (γ) of each downstream stator blade of the second type in dependence on an incidence phase of operation of the aeronautical thruster. 
     
     
         20 . A method of operating the propulsion system according to  claim 16 , the method comprising adjusting the pitch angle (γ) of each downstream stator blade of the second type in dependence on an incidence phase of operation of the aeronautical thruster.